Primary hyperoxaluria Type 1 (“PH1”) is a rare autosomal recessive inborn error of glyoxylate metabolism, caused by a deficiency of the liver-specific enzyme alanine:glyoxylate aminotransferase. The disorder results in overproduction and excessive urinary excretion of oxalate, causing recurrent urolithiasis and nephrocalcinosis. As glomerular filtration rate declines due to progressive renal involvement, oxalate accumulates leading to systemic oxalosis. The diagnosis is based on clinical and sonographic findings, urine oxalate assessment, enzymology and/or DNA analysis. While early conservative treatment has aimed to maintain renal function, in chronic kidney disease Stages 4 and 5, the best outcomes to date have been achieved with combined liver-kidney transplantation (Cochat et al. Nephrol Dial Transplant 27: 1729-36).
PH1 is the most common form of primary hyperoxaluria and has an estimated prevalence of 1 to 3 cases per 1 million population and an incidence rate of approximately 1 case per 120,000 live births per year in Europe (Cochat et al. Nephrol Dial Transplant 10 (Supp) 8): 3-7; van Woerden et al, Nephrol Dial Transplant 18: 273-9). It accounts for 1 to 2% of cases of pediatric end-stage renal disease (ESRD), according to registries from Europe, the United States, and Japan (Harambat et al. Clin J Am Soc Nephrol 7: 458-65), but it appears to be more prevalent in countries in which consanguineous marriages are common (with a prevalence of 10% or higher in some North African and Middle Eastern nations; Kamoun and Lakhoua Pediatr Nephrol 10: 479-82; see Cochat and Rumsby N Engl J Med 369(7):649-58),
Glycolate oxidase (the product of the HAO1, for “hydroxyacid oxidase 1”, gene) is the enzyme responsible for converting glycolate to glyoxylate in the mitochondrial/peroxisomal glycine metabolism pathway in the liver and pancreas. While glycolate is a harmless intermediate of the glycine metabolism pathway, accumulation of glyoxylate (via, e.g., AGT1 mutation) drives oxalate accumulation, which ultimately results in the PH1 disease.
Double-stranded RNA (dsRNA) agents possessing strand lengths of 25 to 35 nucleotides have been described as effective inhibitors of target gene expression in mammalian cells (Rossi et al., U.S. Pat. No. 8,084,599 and U.S. Patent Application No. 2005/0277610). dsRNA agents of such length are believed to be processed by the Dicer enzyme of the RNA interference (RNAi.) pathway, leading such agents to be termed “Dicer substrate siRNA” (“DsiRNA”) agents. Additional modified structures of DsiRNA agents were previously described (Rossi et al., U.S. Patent Application No. 2007/0265220), Effective extended forms of Dicer substrates have also recently been described (Brown, U.S. Pat. Nos. 8,349,809 and 8,513,207).